1. Field of the Invention
The invention relates generally to the field of photography and particularly to a film cassette containing roll film.
2. Description of the Prior Art
In conventional 35 mm film manufacturers' cassettes, such as manufactured by Eastman Kodak Co. and Fuji Photo Film Co., Ltd., the filmstrip is wound on a flanged spool which is rotatably supported within a hollow cylindrical shell. A free leading end section of the filmstrip approximately 21/3 inches long, commonly referred to as a "film leader", protrudes from a light-trapped slit or mouth formed between a pair of throat portions of the cassette shell. One end of the spool has a short axial extension which projects from the shell, enabling the spool to be turned by hand. If the spool is initially rotated in an unwinding direction, the film roll inside the shell will tend to expand radially since the inner end of the filmstrip is attached to the spool, and the fogged leader section protruding from the slit will remain stationary. The film roll can expand radially until a non-slipping relation is established between its outermost convolution and the inner curved wall of the shell. Once this non-slipping relation exists, there is a binding effect between the film roll and the shell which prevents further rotation of the spool in the unwinding direction. Thus, rotation of the spool in the unwinding direction cannot serve to advance the filmstrip out of the shell, and it is necessary in the typical 35 mm camera to engage the protruding leader section to draw the filmstrip out of the shell.
A 35 mm film cassette has been proposed which, unlike conventional film cassettes, includes a film leader that does not extend outside the cassette shell. The film leader, instead, is located entirely within the cassette shell. Specifically, in U.S. Pat. No. 4,423,943, granted Jan. 3, 1984, there is disclosed a film cassette wherein the outermost convolution of the film roll wound on the film spool is radially constrained by respective circumferential lips of two axially spaced flanges of the spool to prevent the outermost convolution from contacting an inner wall of the cassette shell. A trailing end section of the filmstrip is secured to the film spool, and the leading end section of the filmstrip is reduced in width to allow it to protrude from between the circumferential lips and rest against the shell wall. During initial unwinding rotation of the film spool, the leading end section of the filmstrip is advanced automatically to and through a film passageway opening in order to exit the cassette shell. The passageway opening has a width that is slightly less than the width of the filmstrip, which results in the filmstrip being transversely bowed as it is uncoiled from the film spool, and thereby facilitates movement of the film edges under the circumferential lips of the respective flanges. Thus, all that is needed to advance the leading end section of the filmstrip to the outside of the cassette shell via the passageway opening is to rotate the film spool in an unwinding direction. However, transverse bowing of the filmstrip to move its edges under the circumferential lips of the respective flanges results in increased friction between the filmstrip and the cassette structure which will impede advance of the filmstrip from the cassette shell and may damage the filmstrip.